There are many industrial and municipal facilities that produce waste waters or like liquids having organic constituents. The organic constituents can be a significant source of pollution unless the waste waters are properly treated. Also the organic constituents may include a wide variety of products that would be useful if properly recovered.
It has been known for many years that under aqueous alkaline conditions, and relatively high pressures and temperatures, oxygen will break down organic molecules, i.e. oxidize them. There have been great difficulties in effectively utilizing this information, however, since the oxygen reaction that takes place produces organic acids, particularly from the production of carbon dioxide in the reaction. The organic acids neutralize the alkali and the reaction rate drops dramatically. Excessive amounts of alkali are thus needed to maintain satisfactory reaction rates, rendering such a procedure impractical.
According to the present invention, the problem of neutralization of the alkali is specifically dealt with by continuously and immediately removing the gaseous acidic products from the waste water so that they do not significantly contribute to lowering of the pH of the waste water, so that the reaction can proceed without the necessity of adding substantial additional alkali. This desirable result can be achieved according to the invention by utilizing known, or readily constructed, equipment.
One way to affect continuous and immediate removal of the gaseous acidic products is to utilize a gas sparged hydrocyclone, such as disclosed in the U.S. parent application Ser. No. 07/573,975, filed Aug. 28, 1990 (the disclosure of which is hereby incorporated by reference herein), or by utilizing the gas sparged hydrocyclone such as shown in co-pending U.S. application Ser. No. 07/573,978, filed Aug. 28, 1990 (the disclosure of which is hereby incorporated by reference herein). Alternatively, according to the invention the continuous and immediate removal of gaseous acidic products may be accomplished utilizing a reactor comprising a pressurized vertical vessel having a downwardly extending spiral surface therein over which the liquid to be treated flows in a thin film. Carbon dioxide, or like gaseous acidic products, are removed from a central portion of the spiral, while oxygen containing gas is introduced at the bottom of the vessel and/or at various intermediate points.
According to one aspect of the present invention, a method of oxidizing organic constituents in a liquid is provided, comprising the following steps: (a) If the liquid is not already alkaline, adding sufficient alkali to the liquid to render it alkaline. (b) Continuously reacting the organic constituents in the liquid with an oxygen containing gas at pressure and temperature conditions such that oxidized organics and gaseous acidic products of oxidation are produced. And, (c) continuously and immediately removing the gaseous acidic products from the liquid so that they do not significantly contribute to lowering of the pH of the liquid, so that the reaction in step (b) may proceed, the liquid remaining alkaline without the necessity of adding substantial additional alkali.
Steps (b) and (c) may be practiced by: (i) Introducing the liquid into the first end of a vortex. (ii) Introducing gas containing at least the oxygen content of ambient air from exteriorly of the vortex into contact with the liquid in the vortex. (iii) Removing treated liquid from the second end of the vortex, opposite the first end. And, (iv) removing gaseous acidic products from the first end of the vortex, at a non-liquid containing portion thereof.
Alternatively, steps (b) and (c) may be practiced by: (i) Causing the liquid to flow in a thin film in a downwardly extending spiral path, having a center portion in which essentially no liquid flows. (ii) Introducing gas containing at least the oxygen content of ambient air into intimate contact with the liquid as in flows in the spiral path. (iii) Removing treated liquid from the bottom of the path. And, (iv) removing gaseous acidic products from the center portion of the spiral path, at the top thereof.
Steps (b) and (c) may be further practiced, prior to step (i), by holding the liquid within a volume at a pressure greater than 10 psig and a temperature of greater than 100.degree. C., introducing the gas having an oxygen at least as great as that of ambient air into the volume, and removing gaseous acidic products from the volume. Step (b) may be practiced utilizing air, and there may be the further steps, after step (c), of: (d) Continuously reacting the organic constituents in the liquid with a gas containing at least about 90% oxygen at pressure and temperature conditions such that oxidized organics and gaseous acidic products of oxidation are produced. And, (e) continuously and immediately removing the gaseous acidic products from the liquid so that they do not significantly contribute to lowering of the pH of the liquid, so that the reaction in step (d) may proceed, the liquid remaining alkaline without the necessity of adding additional alkali. After step (e), there may be the further step of treating the liquid with ozone (e.g. a mixture of ozone and carbon dioxide, or like beneficiating gas).
A wide variety of waste waters may be treated according to the present invention, such as bleach plant extraction stage liquor, which contains sodium ions. Byproducts may be recovered from the liquid, such as recovery of the sodium ions for use elsewhere in the pulp plant.
The liquid may be rendered alkaline by adding lime to it. Prior to reacting it with oxygen, the liquid may also be clarified, and a catalyst may be added to the liquid prior to, or contemporaneously with, the addition of oxygen thereto (e.g. iron may be added as a catalyst). While the pressure and temperature will vary greatly, and be dependent upon the particular liquid and organic constituents therein, the typical pressure range is about 10-200 psig, with a typical temperature range of about 100-200.degree. C. While air may be utilized as the oxygen containing gas, air enriched with oxygen (e.g. 50% oxygen), or in some situations a gas containing at least about 90% oxygen, can be utilized.
The method of oxidizing organic constituents in a liquid utilizing a gas sparged hydrocyclone is also contemplated. That method comprises the following steps (a) If the liquid is not already sufficiently alkaline for the organic constituents therein to be readily oxidized, adding sufficient alkali thereto to render it sufficiently alkaline. (b) Introducing the liquid into the first end of a vortex. (c) Introducing gas containing at least the oxygen content of ambient air from exteriorly of the vortex into contact with the liquid in the vortex at pressure and temperature conditions such that oxidized organics and gaseous acidic products of oxidation are produced. (d) Removing treated liquid from the second end of the vortex, opposite the first end; and (e) removing gaseous acidic products from the first end of the vortex, at a non-liquid containing portion thereof.
The invention also relates to a novel reactor. The reactor according to the invention comprises the following components: A pressurized generally vertical vessel. A downwardly extending stationary spiral surface having a top, horizontal center, and bottom, and mounted in the vessel, substantially concentric therewith. Vertically aligned conduit means mounted at the horizontal center of vertically spaced portions of the spiral surface. A liquid inlet at the top of the vessel adjacent the top of the spiral surface. A liquid outlet from the bottom of the vessel, adjacent the bottom of the spiral surface. Gas removal means adjacent or above the liquid inlet at the top of the vessel. And, gas introducing means for introducing gas into the vessel below the liquid inlet. Surface manifestations may be provided on the spiral surface for enhancing mixing of liquid flowing over the surface with surrounding gas. The surface manifestations may be projections or roughened portions. The gas introduction may take place at the bottom of the vessel and/or at at least one point above immediately adjacent the spiral surface, with a velocity vector directing the gas toward the liquid.
It is the primary object of the present invention to provide for effective and efficient oxidation of organic constituents in a liquid, or other beneficiating action. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.